Sapwood Temperatures in Hemlock Trees at Harvard Forest HEM Tower 1997-1998

Sapwood temperatures in four large hemlocks, 130-200 years old and about 40 to 90 cm basal diameter and 25 to 29 m tall, were measured in order to estimate sapwood respiration in these trees as part of a physiological model for hemlock forest carbon exchange. As expected, sapwood temperature varied most in small branches and least in the main bole of the tree near the ground. An additional finding from these measurements is that sapwood begins to freeze at -1 to -2 degrees C, as shown by a stabilization and in some cases an increase of about 1 degree C in sapwood temperature when air temperature cooled continuously to below this temperature range.

为开展铁杉林碳交换生理模型相关研究，本研究对4株树龄130~200年、基径40~90 cm、株高25~29 m的成熟铁杉的边材温度进行了测定，以估算其边材呼吸速率。正如预期，边材温度的波动幅度在细枝中最大，而在靠近地面的树干主茎中最小。本次测量的另一项发现为：边材的起始冻结温度为-1~-2℃，当空气温度持续降至该温度区间以下时，边材温度会出现平稳阶段，部分情况下还会升高约1℃，该现象可验证这一结论。